The basements of many residential buildings are constructed with drainage systems to carry rain water away from the foundation. Such systems, required by many local building codes, keep the basement dry and prevent wall and floor damage due to running water and high localized humidity.
A basement is a building foundation which is excavated into the earth. Walls of brick, block or poured concrete support the above-ground structure of the building and the floor is usually formed of poured concrete.
Clay drain tiles, or perforated plastic pipes are installed around the perimeter walls to collect rain water which drains through the soil. These tiles are laid in a bed of gravel or sand, the porosity of which aids the drainage of water from the surrounding soil. The collecting tiles are laid with a slope which allows gravity to induce flow.
The water flows from the collecting tiles to the sump, which is a small pit in one corner of the basement. This pit is excavated below level of the collecting tiles, well below basement floor level.
Drainage systems have enabled the use of basements as additional storage, recreation and even living space. Wood paneled walls and carpeted floors are commonplace in basement recreation rooms. Most need to be protected from water damage by a reliable, properly operating system.
Such a system depends on an electric motor to drive a pump, usually a centrifugal pump, which lifts the water from a collecting sump. The pump is usually called on to operate only during heavy rainfalls and pump water away from the foundation through a hose to a drain field. In conventional systems, a water-level sensor is used to automatically turn the pump on when the sump fills to a predetermined high water level and stop the pump when the water level drops below a predetermined low water level.
Significantly, loss of utility-provided electric power renders the system inoperative unless special precautions are taken. If the power outage persists, water damage to the basement may be the result. The likelihood of such damage is aggravated by the typical coincidence of electric power outages with storms and heavy rainfall. To ensure protection of the basement and its contents from water damage, an uninterruptable power supply to the pumping system is required.
A brochure by Aquanot Co. describes a sump pump system using an AC-to-DC converter and a single 12 VDC motor to drive the sump pump from either the 60 Hz utility line or a 12 VDC battery. It can be used either as a standby system (to supplement a conventional AC system including motor) or it can be used as the primary system. According to the brochure, the control provides 14 amp. at 12 VDC (nominally 170 watts during battery or "emergency mode" operation) or 3.5 amp. at 120 VAC (nominally 420 watts during normal operation). Based solely on this data, it appears likely that the Aquanot system operates the pump at a greater pumping rate during normal operation than during battery operation.
A brochure describing the Glentronics Basement Watchdog system indicates that it is microprocessor controlled and uses a single pump motor for both normal and emergency operation. The brochure explains that the controller has a quick battery recharge feature and also shuts off the battery "trickle charge" when the battery reaches some predetermined voltage level. This suggests that two different charging rates are used in the Glentronics system.
The pump motor of the Glentronics system is understood to be rated 12 VDC and starts "across the line," i.e., without a soft start. Motor current is understood to be the same, irrespective of whether the motor is powered form the AC line or from the battery.
Product brochures by Basement Flood Protector, Wayne Scott Fetzer, F. E. Myers Water Ace, Simer and Expert describe sump pump systems used as standby systems only and incorporate motors and pumps separate from those of the conventional system. All use DC motors and standby batteries. Systems incorporating batteries typically use an automotive-type 12 VDC battery because of their low cost and wide availability.
U.S. Pat. No. 3,726,606 (Peters) shows a conventional two-pump, two-motor sump pump system. The apparatus shown in U.S. Pat. No. 4,672,520 (Ueda et al.), a current-source apparatus, includes a converter, a battery as a source of standby power, a current source inverter and a three phase electric motor. The battery in the Ueda et al. apparatus is connected on the AC line side of the converter rather than between the converter and the inverter. No charging circuit is described and when operating in a battery-powered mode, power to the motor is intermittent. Capacitors are coupled in parallel across the terminals of the three phase motor and while the apparatus is clearly microprocessor controlled, the control appears to extend only to gate control.
The uninterruptible power supply (UPS) apparatus shown in U.S. Pat. No. 4,709,318 (Gephart et al.) is a fixed-frequency, fixed-voltage, single-phase UPS system. It is intended for use with personal computers or similarly technically sophisticated instrumentation as a back-up power source. It includes an AC-to-DC converter, a DC-to-DC converter and what the patents calls a DC-to-AC converter arranged in that order from input to load.
While systems of the foregoing types have been generally satisfactory and widely used to drive sump pumps, they tend to be characterized by certain disadvantages. For example, their battery re-charging systems tend to boil the water out of the battery after several months on standby, leaving the battery inoperable when eventually called to emergency duty. And they do not recharge quickly, so multiple outages in succession can result in system failure.
A DC motor, with its brushes and commutator, is not well suited to sump pump applications. A commutator has a limited life due to friction and wear and life may be further shortened by high humidity and resulting corrosion. Further, DC motors incorporate cost unnecessary in an AC machine in that construction, machining and polishing of the commutator is relatively expensive. And DC motors use relatively-expensive "exotic" permanent magnet materials.
Another disadvantage is that pump drive motors are started "across the line" and accelerate to operating speed in a small fraction of a second. Across-the-line starting is more abusive to the structure of the pump and motor alike (the latter resulting from elevated starting current) than is "soft" (controlled acceleration) starting and the resulting clearly-audible "water hammer" noise can be distracting.
Yet another disadvantage is that such systems are incapable of modulating motor speed generally consistent with the rate of water flow into the sump. That is, they start and stop frequently, thereby unnecessarily abusing the motor and pump and creating unwanted noise.
Still another disadvantage relates to the fact that the life of an automotive-type lead acid battery is shortened when the battery goes unused for long periods. But known systems do not address this problem by providing, for example, a battery "exercise" feature to periodically draw energy from the battery and later re-charge it.